Blood coagulation and fibrinolysis are complex multi-step processes which can both be initiated by cell-associated factors. Tissue factor (thromboplastin) is a potent cellular procoagulant which forms a complex with the circulating enzyme factor VII to initiate coagulation. Plasminogen activator is a cell-associated enzyme which cleaves circulating plasminogen to the fibrinolytic enzyme plasmin. Many cells also possess inhibitors of coagulation and fibrinolysis. We propose to study the control of cellular procoagulant and fibrinolytic agents, and their inhibitors. We have purified to homogeniety a stimulatory substance from platelets which increases both tissue factor and the level of fibrinolytic inhibitors in fibroblasts. We will study how this platelet-derived stimulatory substance interacts with cells grown in tissue culture and how it is metabolized or degraded; the level of this material in patients known to be at higher risk for the development of cardiovascular disease will also be studied. The stimulation by the platelet-derived material of both procoagulant and fibrinolytic activity suggest that both activities may share common control processes at the cellular level. We will explore this possibility further using other stimulatory substances. We have shown that the arachidonic acid metabolites derived via lipoxygenase are involved in the control of plasminogen activator levels. We will use specific inhibitors and purified lipoxygenase pathway products to examine the possibility that such products are also be involved in the regulation of tissue factor. Our studies on the control of plasminogen activator have shown that these are at least 2 pathways for its regulation; one is serum-independent while the second, activated by prostaglandins and catecholamines, requires a serum cofactor(s). We will purify this cofactor(s). The role of lipoxygenase pathway products and cyclic AMP as modulators in the serum-dependent pathway will be studied. Finally, we will continue our purification and characterization of a factor Xa inhibitor from HeLa cells and study the possibility that a similar inhibitor may also be responsible for the very low apparent tissue factor procoagulant activity of vascular endothelial cells.